This invention relates to a data carrier with a security printed image and to a printing plate for producing such a printed image.
For producing high-quality printed products such as bank notes, shares or the like one frequently uses intaglio printing for forgery protection since the printing plate production is very elaborate and expensive and this method produces a very characteristic printed image which cannot be imitated using other printing methods.
In intaglio printing, areal representations are produced by closely adjacent engraved lines, the individual engraved lines normally being fractions of a millimeter wide and being separated by unengraved lands.
For the printing operation the engraved lines of the printing plate are filled with ink. Excess ink is removed from the printing plate with the aid of a wiping cylinder or doctor blade such that only the engraved lines are filled with ink. This wiping process thus removes all ink components on the printing plate surface.
In the printing operation the data carrier to be printed, normally paper, is finally pressed onto the printing plate at high pressure by means of a pressure cylinder with an elastic surface. The data carrier is thereby pressed into the ink-filled engraved lines of the printing plate, thus coming in contact with the ink. When the data carrier is detached it pulls the ink out of the depressions of the engraved lines. The thus produced printed image has printed lines which vary in ink layer thickness depending on the depth of the engraving.
If one uses transparent inks in intaglio printing one obtains a light tint when printing a white data carrier with small ink layer thicknesses, and darker tones when printing with thick ink layers. In comparison with other common printing methods, intaglio printing can produce printed images with very great ink layer thicknesses. The resulting printed images are even manually tactile if accordingly deep engravings are used. The use of accordingly fine engravings also permits extremely fine, very sharp printed lines.
WO 97/48555 describes a method for producing intaglio printing plates in reproducible, machine-made fashion and permitting line width and line depth to be adjusted largely independently of each other. For this purpose the lines of a line original are detected and the surface area of each line exactly determined. With an engraving tool, for example a rotating chisel or a laser beam, the outside contour of said surface area is first engraved in order to cleanly outline the surface area. The outlined area of the surface area is subsequently cleared out using the same or another engraving tool so that the total line is exactly engraved in accordance with the line original. In this way one can also produce very narrow lines with a relatively great engraving depth, i.e. high inking on the data carrier. This makes even very fine lines tactile as reliefs.